1. Field of Invention
The invention relates to a development apparatus for printing apparatuses and machines.
2. Description of Related Art
Generally, electrophotographic printing includes charging a photoconductive member to a substantially uniform potential. This sensitizes the surface of the photoconductive member. The charged portion of the photoconductive surface is then exposed to a light image from either a modulated light source or from light reflected from an original document being reproduced. This creates an electrostatic latent image on the photoconductive surface. After the electrostatic latent image is created on the photoconductive surface, the latent image is developed. Two component and single component developer materials are commonly used to develop the electrostatic latent image.
A typical two component developer comprises magnetic carrier granules and toner particles that adhere triboelectrically to the magnetic carrier granules. In contrast, a single component developer material typically comprises only toner particles. The toner particles are attracted to the latent image recorded on the photoconductive surface to form a developed image on the photoconductive surface. The developed image is then transferred to a copy sheet. Subsequently, the toner powder image is heated to permanently fuse the toner powder image to the copy sheet.
One method to transport toner particles in a development system in a manner that ensures a uniform dispersion of the toner particles on the resulting copy page is through the use of traveling waves. For example, U.S. Pat. No. 4,647,179 to Schmidlin, incorporated herein by reference in its entirety, generates a traveling wave by alternating voltages of three or more phases applied to a linear array of conductors placed about the outer perimeter of a toner particle conveyor. In this development apparatus, the force F for moving the toner particles about the conveyor is equal to QE.sub.t, where Q is the charge on the toner particles and E.sub.t is the tangential force supplied by multiphase alternating current voltage applied to the array of conductors.
A magnetic brush supplies toner particles to the conveyor. The magnetic brush rotates in the same direction as the traveling wave. This gives an initial velocity to the toner particles that enables toner particles having a much lower charge to be propelled by the wave sufficiently to reach the charged photoconductor surface.
Another apparatus for transporting charged toner particles in a predetermined path is disclosed in U.S. Pat. No. 5,893,015 to Mojarradi et al., incorporated herein by reference in its entirety. The incorporated 015 patent discloses an apparatus that includes a donor member adapted to move charged particles on its surface in a predetermined path. The donor member includes an electrode array on its outer surface. The electrode array includes a plurality of spaced apart electrodes extending substantially across the width of the surface of the donor member. The 015 patent further discloses a multiphase direct current voltage source operatively coupled to the electrode array. The phases are shifted with respect to each other to create an electrodynamic wave pattern capable of moving charged particles on the surface of the donor member in a predetermined path.